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ServoMotor Installing

Installing a Servo Motor on a C-Band Satellite System

In the United States, Canada and other parts of the world, satellite-based transmissions are sent in two kinds of polarities: horizontal and vertical. These two kinds of polarities keep adjacent channels from interfering with one another. On a receiving satellite system there must either be a mechanical antenna that is positioned to receive the desired polarity (channel) or there are two fixed antenna "probes" in each polarity plane and one of them is electronically selected by changing the voltage going to the LNBF.

On most C-Band satellite systems, the polarity is selected mechanically. The part that physically moves the receiving antenna is a small servo motor that is mounted to the feedhorn (the part that points at the face of the dish) and changes the polarity every time that you change channels. This servo motor also has an integrated circuit in it and many other static electricity sensitive components, which make it prone to being damaged by lightning. There are several different versions of servo motors on the market and most have a poor failure rate. This is why we only sell Astrotel which is fully tested before shipping and has a 1-year warranty.

Changing The Servo Motor

On most satellite systems, this servo motor can be changed in less than 15 minutes. To change this part you will need:
  • A small phillips screwdriver that has a shaft length of about 3" or more.
  • A flat screwdriver or knife
  • Pliers
  • Wire cutters

Step 1:
Using the wire cutters, individually cut the three wires connecting the servo motor to the satellite cable near the servo motor.

Step 2:
Remove the four philips machine screws holding the servo motor to the feedhorn.

Step 3:
Using the flat screwdriver or knife, scrape any rubber or silicone that may be on the surface of the feedhorn where the old servo motor was mounted.

Step 4:
Mount the new servo motor to the feedhorn with the original four machine screws that the old servo motor was mounted with.

Step 5:
Connect the three individual wires coming out of the new servo motor to the satellite cable using the Insulation Displacement Connectors that are provided. These unique 3M connectors don't require stripping the insulation off of any of the wires. All you do is insert the two wires (one from the servo motor and one from the satellite cable) into the Insulation Displacement Connector and then take the pliers and squeeze the connector. When you do this, silicone grease will seal the connection helping to reduce corrosion. Continue this procedure with the remaining pairs of wires.

Installation Notes:

If a picture comes in really quick and then gets snowy again when changing channels on the satellite receiver after the installation of the servo motor, there is a good chance that you will need to manually rotate the black plastic insert in between the actual servo motor and the round plastic piece holding the feedhorn antenna.

To do this, go back out to the dish and remove the four philips screws holding the servo motor to the feedhorn and simply pull off this round plastic piece and rotate it 90. This piece will be 3/4" wide and have a raised "slot" going diagonally through it. Then reinstall the servo motor. The channels should then come in as they normally did before the old servo motor went out.

If some or all of the channels still don't come in very clear, then you may need to fine tune the "skew" or polarity with your satellite receiver.

This article was published on Tuesday 14 December, 2004.
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